The present invention relates to an electron emission element for emitting electrons and a method for producing the same. In particular, the present invention relates to an electron emission element formed by using diamond particles and a method for producing the same. Furthermore, the present invention relates to an electron emission source constructed by using a plurality of electron emission elements and an image display apparatus utilizing the same.
In recent years, as an electron beam source replacing an electron gun for a thin display with high definition and an electron source of a vacuum microelectronic device capable of operating at a high speed, a micro-electron emission element of a micron size has been paid attention to. There are various types of electron emission elements. In general, a field emission type (FE type), a tunnel injection type (MIM type or MIS type), a surface conduction type (SCE type), or the like have been reported.
In the FE type electron emission element, a voltage is supplied to a gate electrode to apply an electric field to an electron emission portion, whereby electrons are emitted from a cone-shaped projected portion formed of silicon (Si) or molybdenum (Mo). In the MIM type or MIS type electron emission element, a layered structure including metal, an insulating layer, a semiconductor layer, and the like is formed, and electrons are injected to and passed through the insulating layer from the metal layer by utilizing a tunnel effect, whereby electrons are output from an electron emission portion. Furthermore, in the SCE type electron emission element, an electric current is allowed to flow in an in-plane direction of a thin film formed on a substrate, and electrons are emitted from a previously formed electron emission portion (generally, a microcrack portion present in a conducting region of the thin film).
Any of the above-mentioned elements are characterized in that their structures can be miniaturized and integrated by using a micro-processing technique.
In general, it is required that a material for an electron emission portion of an electron emission element has characteristics of: (1) being likely to emit electrons in a relatively small electric field (i.e., being capable of emitting electrons efficiently), (2) having good stability of an electric current to be obtained, (3) having a small change in electron emission characteristics with passage of time, and the like. However, in the above-mentioned conventional electron emission elements which have been reported, their operating characteristics are largely dependent upon the shape of an electron emission portion, and greatly change with passage of time. Furthermore, it is difficult to produce such electron emission elements with good reproducibility, and it is very difficult to control their operation characteristics.
As is understood from the above, a structure of a conventional electron emission element or a structure and a material of an electron emission portion included therein do not satisfy required characteristics sufficiently.
The present invention has been achieved so as to overcome the above-mentioned problems, and its objective is to provide: (1) an electron emission element with high stability, capable of emitting electrons efficiently, by dispersing a plurality of electron emission portions made of a particle or an aggregate of particles; (2) a high-efficiency electron emission source and an image display apparatus using the same, by disposing a plurality of the above-mentioned electron emission elements; (3) an electron emission element and an electron emission source capable of emitting electrons efficiently, in particular, by using diamond particles for an electron emission member; (4) an image display apparatus comprised of an electron emission source including a plurality of electron emission elements capable of emitting electrons efficiently and an image forming member, and a flat display for displaying a bright and stable image; (5) a production method capable of easily and efficiently conducting an important production process with respect to diamond particles used for an electron emission portion in an electron emission element of the present invention; and (6) a method for producing an electron emission element capable of producing an electron emission element having an electron emission portion, which stably operates, over a large area with ease and good reproducibility, by conducting a step of uniformly distributing diamond particles.
An electron emission element of the present invention includes: a pair of electrodes disposed in a horizontal direction at a predetermined interval: and a plurality of electron emission portions disposed so as to be dispersed between the pair of electrodes.
In an embodiment, the above-mentioned electron emission element further includes a substrate having an insulating surface, wherein the pair of electrodes and the plurality of electron emission portions are disposed on the insulating surface of the substrate. More specifically, electrons move from one of the electrodes to the other electrode so as to hop through the plurality of electron emission portions by a transverse electric field generated between the pair of electrodes.
In another embodiment, the above-mentioned electron emission element further includes a conductive layer disposed between the pair of electrodes and electrically connected thereto, wherein the plurality of electron emission portions are disposed on the conductive layer. For example, the pair of electrodes can be provided as partial regions on ends of the conductive layer. Alternatively, the pair of electrodes and the conductive layer are made of different materials. In any case, electrons move from one of the electrodes to the other electrode by an electric current flowing through an inside of the conductive layer in an in-plane direction.
The conductive layer can be heated when an electric current flows through an inside of the conductive layer in an in-plane direction.
An amount of electron emission can be modulated by controlling an amount of the electric current flowing through an inside of the conductive layer in an in-plane direction.
Preferably, a dispersion density of the plurality of electron emission portions is about 1xc3x97109/cm2 or more.
Preferably, the plurality of electron emission portions are independent relative to one another without coming into contact with each other.
Each of the plurality of electron emission portions is made of a particle of a predetermined material or an aggregate of the particles.
Preferably, an average particle diameter of the particles included in each of the plurality of electron emission portions is about 10 xcexcm or less.
The predetermined material is diamond or a material mainly containing diamond.
The above-mentioned electron emission element includes a structure in which atoms on an outermost surface of the diamond or the material mainly containing diamond are terminated by binding to hydrogen atoms. Preferably, an amount of the hydrogen atoms binding to the atoms on the outermost surface is about 1xc3x971015/cm2 or more.
The diamond or the material mainly containing diamond has crystal defects. Preferably, a density of the crystal defects is about 1xc3x971013/cm3 or more.
The diamond or the material mainly containing diamond has a non-diamond component which is less than about 10% by volume.
The particles of the predetermined material are diamond particles produced by crushing a diamond film formed by a vapor-phase synthesis method. For example, the vapor-phase synthesis method is a plasma jet CVD method.
The conductive layer is a metal layer or an n-type semiconductor layer.
Preferably, a thickness of the conductive layer is about 100 nm or less.
Preferably, an electric resistance of the conductive layer is higher than an electric resistance of the electron emission portions.
An electron emission source includes a plurality of electron emission elements arranged in a predetermined pattern in such a manner as to emit electrons in accordance with an input signal to each of the electron emission elements, and each of the plurality of electron emission elements is the element having the above-mentioned characteristics.
Preferably, the above-mentioned electron emission source further includes a plurality of lines in a first direction electrically insulated from each other and a plurality of lines in a second direction electrically insulated from each other, wherein the plurality of lines in the first direction and the plurality of lines in the second direction are disposed in directions so as to be orthogonal to each other, and each of the electron emission elements is disposed in the vicinity of each intersection between the lines in the first direction and the lines in the second direction.
An image display apparatus provided according to the present invention includes an electron emission source and an image forming member for forming an image upon irradiation with electrons emitted from the electron emission source, wherein the electron emission source has the above-mentioned characteristics.
A method for producing an electron emission element of the present invention includes the steps of: disposing a pair of electrodes in a horizontal direction at a predetermined interval; and dispersively disposing a plurality of electron emission portions between the pair of electrodes.
In an embodiment, the above-mentioned production method further includes the step of providing a substrate having an insulating surface, wherein the pair of electrodes and the plurality of electron emission portions are disposed on the insulating surface of the substrate.
Furthermore, the above-mentioned production method further includes the step of providing a conductive layer between the pair of electrodes so as to be electrically connected thereto, wherein the plurality of electron emission portions are disposed on the conductive layer.
The pair of electrodes can be provided as partial regions on ends of the conductive layer. Alternatively, the pair of electrodes and the conductive layer are made of different materials.
The above-mentioned dispersively disposing step includes the step of dispersively disposing particles of a predetermined material or an aggregate of the particles as the plurality of electron emission portions.
For example, the above-mentioned dispersively disposing step includes the steps of: applying a solution or a solvent in which the particles of the predetermined material are dispersed; and removing the solution or the solvent. Alternatively, the above-mentioned dispersively disposing step includes the step of applying an ultrasonic vibration in a solution or a solvent in which the particles of the predetermined material are dispersed.
The predetermined material is diamond or a material mainly containing diamond.
In this case, the dispersively disposing step may include the step of distributing the diamond particles using a solution in which diamond particles are dispersed. Alternatively, the above-mentioned distributing step includes the step of applying an ultrasonic vibration in the solution in which the diamond particles are dispersed.
Preferably, an amount of the diamond particles dispersed in the solution is about 0.01 g to about 100 g per liter of the solution. Alternatively, the number of the diamond particles dispersed in the solution is about 1xc3x971016 to about 1xc3x971020 per liter of the solution.
Preferably, a pH value of the solution in which the diamond particles are dispersed is about 7 or less.
The solution in which the diamond particles are dispersed may contain at least fluorine atoms. Alternatively, the solution in which the diamond particles are dispersed contains at least hydrofluoric acid or ammonium fluoride.
In an embodiment, the above-mentioned production method further includes the step of allowing atoms on an outermost surface of the diamond particles to bind to hydrogen atoms.
Diamond particles heat-treated at about 600xc2x0 C. or more in an atmosphere containing hydrogen gas can be used in the hydrogen binding step. Alternatively, the hydrogen binding step may include the step of heating the diamond particles at 600xc2x0 C. or more in an atmosphere containing hydrogen or the step of irradiating with ultraviolet light.
Alternatively, the hydrogen binding step may include the step of exposing the diamond particles to plasma containing at least hydrogen under a state where a temperature of the diamond particles is about 300xc2x0 C. or more.
In an embodiment, the above-mentioned production method further includes the step of introducing crystal defect into the diamond particles.
Diamond particles of which surfaces are irradiated with accelerated particles can be used in the defect introducing step. Alternatively, the defect introducing step includes the step of irradiating the diamond particles with accelerated atoms.
In an embodiment, the above-mentioned production method further includes the step of additionally growing diamond on the distributed diamond particles.
A vapor-phase synthesis process of diamond can be used in the additional growth step.
A method for producing an electron emission source provided according to the present invention includes the steps of: arranging a plurality of electron emission elements in a predetermined pattern in such a manner that the electron emission elements emit electrons in accordance with an input signal to each of the electron emission elements: and forming each of the plurality of electron emission elements by the production method having the above-mentioned characteristics.
The above-mentioned method for producing an electron emission source includes the steps of: disposing a plurality of lines in a first direction electrically insulated from each other and a plurality of lines in a second direction electrically insulated from each other in such a manner that the plurality of lines in the first direction and the plurality of lines in the second direction are orthogonal to each other; and disposing each of the electron emission elements in the vicinity of each intersection between the lines in the first direction and the lines in the second direction.
A method for producing an image display apparatus provided according to the present invention includes the steps of: constructing an electron emission source; and disposing an image forming member for forming an image upon irradiation with electrons emitted from the electron emission source, wherein the electron emission source is constructed by the production method having the above-mentioned characteristics.